Currently, one of the most commonly-used optoelectronic elements is a diode, which can be roughly divided into a light-emitting element, such as a light-emitting diode (LED) and a laser diode (LD), and a photosensitive element, such as a photo-detector or a solar cell, wherein the photo-detector can be a photodiode (PD) or a positive-intrinsic-negative (PIN) diode, etc.
The LED is an element having excellent optoelectronic features of low power consumption, low heat generation, long operation life, good impact resistance, small size, fast responding speed and stable emission wavelength, etc.
Generally speaking, the LED can be applied to the specific purposes of various home appliances and computer equipments, such as computer peripherals, clock displays or instrumental panels. However, with the enhancement of the LED in illumination, brightness and color rendition, the LED display is developed accordingly. The LED display can be used in indoors/outdoors full color bulletin boards, traffic lights, and variable message signs (VMS), etc.
In the conventional technologies, the LED display is composed of a LED array for displaying letters, digits or full color images. The structure of a conventional LED is as shown in FIG. 1. The LED shown in FIG. 1 comprises a coating resin 101, a LED chip 102, a conductive wire 103, a molding material 104, a lead frame 105 and an inner lead 106, wherein the lead frame 105 comprises a base 105a and a lead 105b. The description of the aforementioned LED structure can be referred to U.S. Pat. No. 5,998,925. Hereinafter, the LED structure will be described in details.
Such as shown in FIG. 1, the coating resin 101 is filled in the base 105a to cover the LED chip 102, so as to prevent the LED chip 102 from contacting oxygen or moisture, thereby protecting the LED chip 102. The coating resin 101 is generally made of transparent material, such as epoxy resin, urea resin or glass, etc. However, the thermal expansion coefficient and heat conductivity of the coating resin 101 are apparently different from those of the LED chip 102, so that the heat generated from the imperfect electro-optical conversion is easy to be accumulated on the interface between the coating resin 101 and the LED chip 102, while the optoelectronic element is in operation. Moreover, in the manufacturing process, it is quite important about how to use proper temperature and process for the coating resin 101 to be stably coated on or filled in the area surrounding the LED chip 102, and meanwhile, to assure that no extra chemical reaction between two different materials (the coating resin 101 and the LED chip 102) will occur. However, with the current technology, it usually needs to perform a baking step on the coating resin 101 at 150° C. for about 40 minutes, so as cure the coating resin 101. Hence, for fitting to the current process, the coating resin 101 of high purity has to be selected as the material used for coating or filling, (since some elements are easy to be diffused into semiconductor material to change the original properties of the semiconductor material).
The aforementioned structure also causes another bad influence. As the coating resin 101 is a poor heat conductor, heat is accumulated on the interface between two different materials (the coating resin 101 and the LED chip 102). Due to the difference in the thermal expansion coefficients between the coating resin 101 and the LED chip 102, while the element is in operation, heat accumulated therein causes additional stress exerted on the LED chip 102, wherein the stress is exactly proportional to the interface temperature (which is caused by the accumulated heat). While LED elements are developed towards the applications of high brightness and high power, the aforementioned problem will become more and more serious. Even on the current common applications, since the coating resin 101 and the LED chip 102 are different in material properties, the operation stability and life of the optoelectronic element are affected directly or indirectly.
Further, please refer to FIG. 2, which is a detailed diagram showing the elements around the base 105a, wherein the LED chip 102 is a semiconductor element having a PN junction 107. Hence, when a positive voltage is applied to two electrodes of the LED chip 102, the light of specific wavelength will be emitted from the PN junction 107 of the LED chip 102. In the aforementioned structure, the light emitted by the LED chip 102 towards the base 105a cannot be emitted again to the external, and thus the light emission intensity and efficiency of the entire LED device are affected. However, under the current structure, these shortcomings are inevitable.
Such as shown in FIG. 2, the coating resin 101 is used to fill in the base 105a to cover the LED chip 102, and the coating resin 101 may comprise fluorescent matter, such as phosphor. Besides, the coating resin 101 can be transparent material, such epoxy resin, urine resin or glass, etc. Moreover, the fluorescent matter contained in the coating resin 101 can change the light emission wavelength by the way of energy conversion, and the porosity and coating thickness of the fluorescent matter also affect the color of the colored light emitted after the wavelengths respectively generated by the LED and the fluorescent matter are mixed. However, on one hand, due to the oxidization reaction and the deterioration scheme of the coating resin 101 itself, and on the other hand, due to the temperature influence and the UV light irradiation, the deterioration of the coating resin 101 and phosphor is thus accelerated. When the coating resin 101 is deteriorated and cured because of heat, or is damaged by the UV light in sunshine, the coating resin 101 has the phenomenon of curing and deteriorating. Once the coating resin 101 starts deteriorating, the LED chip 102 covered thereby will be affected and damaged. Especially for the element of which the waveband of light emitted is below that of blue light (wherein the wavelength of emitted light is smaller than 480 nm), because the LED chip thereof has the attribute of spontaneous light-emission, and additionally, the light traveling path thereof is concentrated within a specific angle, resulting in high light emission intensity, consequently, the damage to the coating resin is more sever. With the occurrence of these situations, the LED device has the chance to be functionally retarded.
In U.S. Pat. No. 5,367,441, the frame is filled with scattering bodies, wherein the material of the scattering bodies is similar to that of the coating resin 101 shown in FIG. 2. Hence, the structure used in this conventional technology is the same as that described previously, thus also causing the damage to the LED chip and the conductive wire, resulting in reducing the light permissibility of the coating resin 101, so that the LED is functionally retarded.
Please refer FIG. 1 again. In the process for manufacturing the conventional LED, the LED chip 102 has to first be fixed on the base 105a. Thereafter, the conductive wire 103 is formed between the LED chip 102 and the inner lead 106 in a manner of wiring. Then, the coating resin 101 is filled in the base 105a to cover the LED chip 102 and part of the conductive wire 103. However, errors may occur in the process of fixing the LED chip 102, and the conductive wire 103 may not be able to be formed accurately on the bonding pad of the LED chip 102 while being formed on the LED chip 102, thus causing the LED chip 102 to be nonconductive, resulting in manufacturing a defective LED.
On the other hand, as to a photosensitive element, the photosensitive element can be a photodiode, a PIN diode, a photo crystal or a solar cell. Referring to FIG. 3, FIG. 3 is a schematic diagram showing a conventional photodiode of TO-CAN type. FIG. 3 illustrates a photodiode 110, a base 120, a lead pin 130, a lead pin 132, a metal cover 144, a light-emitting window 154, a conductive wire 180, a jointing solder pad 190 and an insulation part 195, etc., wherein the photodiode 110 is fixed on one surface of the base 120, and the lead pin 130 and the lead pin 132 are connected to the other surface of the base 120 for transmitting electrical signals.
As to the metal-can packaging of the photodiode 110, it means that the metal cover 144 is fitted to the base 120, so as to protect the photodiode 110. Besides, the light-emitting window 154 is inset into the upper surface of the metal cover 144, so that, when the metal cover 144 is fitted to the base 120, an incident light 200 from the external can pass through the light-emitting window 154 and is refracted to become an incident light 202, which is further focused on the photodiode 110. Further, when the metal cover 144 is fitted to the base 120, a space 174 is formed between the metal cover 144 and the base 120, wherein the photodiode 110 is located in the space 174. Moreover, one electrode of the LED 110 is electrically connected to the lead pin 130 via the conductive wire 180, and the other electrode of the photodiode 110 is electrically connected to the lead pin 132 via the base 120. Besides, the insulation material 195 is used to isolate the lead pin 130 from the base 120.
The photodiode 110 is a diode that is sharply sensitive to light. When the light irradiates the photodiode 110, the reverse-current of the photodiode 110 will be enlarged, particularly when the photodiode 110 is mostly operated under the condition of reverse bias, wherein it has to be noted that: since the photodiode 110 is a passive element, if the intensity of the incident light 202 emitted to the photodiode 110 is too low, the noise measured from the photodiode 110 will be very large i.e. the signal/noise ratio (S/N Ratio) will be extremely low. Hence, it is a quite important topic about how to design a better structure of packaging to the best possibility for promoting the operation efficiency of the photodiode 110 of photosensitive type, thereby achieving the purpose of photo-detection.
However, the aforementioned photosensitive element of TO-CAN type has the shortcomings described as follows. At first, the light-emitting widow allowing light to enter is not large on the front-side of the photosensitive element of TO-CAN type. Secondly, upon the front-side light being emitted to the surface of the photosensitive element of TO-CAN type, the light reflected thereby is very strong. Moreover, the total reflection will result in the loss of the incident light. Thus, the incident light intensity actually emitted to the photosensitive element becomes very small due to all kinds of loss. Further, because the light emitted to the photodiode is not focused, therefore, even if the light can smoothly pass through the light-emitting window of TO-CAN to the photodiode, the light still cannot be concentrated totally on the sensing area of the photodiode since the light is too divergent. Hence, if the signal intensity from the sample to be tested is very low, the photodiode will not be able to perform light detection normally, due to the insufficient intensity of incident light received by the photodiode (i.e. the S/N ratio is too low).
To resolve the problems of sever loss and over divergence for the incident light, the process or the structure of the photodiode can be modified. For example, in U.S. Pat. No. 6,278,145, it is stated that the semiconductor manufacturing process of the photodiode has to be modified, but it is not taught that, by means of new design, the optimized structure of the photosensitive element is used to promote the operation efficiency of the element.
To sum up, for the current development of optoelectronic devices, it is an important topic about, how to provide an optoelectronic device to efficiently direct the light emitted by the light-emitting element to the external of the device via the optimum design, thereby promoting the light emission efficiency of the optoelectronic device; or how to effectively concentrate the light emitted to the optoelectronic device on an optoelectronic element, thereby increasing the sensitivity thereof, also preventing the light-emitting element or photosensitive element from being damaged by the coating resin.